1. Technical Field of the Invention
The present invention relates to the formulation of a combination of excipients into pharmaceutical compositions because of their preservative activity, and to the topically applicable pharmaceutical compositions comprising same. The present invention therefore also relates to the combination of excipients having a good preservative activity.
2. Description of Background and/or Related and/or Prior Art
A topical pharmaceutical or cosmetic composition is often a good substrate for the proliferation of microorganisms.
Two major families of microorganisms exist, bacteria and fungi. The European and U.S. pharmacopoeias, that those skilled in the art in the more particular field of pharmaceutical products are duty-bound to follow, have selected, in total, five microorganisms representative of these families, three species of bacteria and two types of fungi.
The following three species of bacteria are representative of the microbial population commonly encountered in contaminations and are capable of causing an infection in humans. Escherichia coli is a gram-negative bacterium. It has a thin wall which is permeable to small molecules. It has a rod shape, known as bacillus. This bacterium is present essentially in fecal waste. Its presence can cause various diseases, such as gastroenteritis. Staphylococcus aureus is a gram-positive bacterium. It therefore has a thicker wall which is impermeable to small molecules. It is spherical in shape and is referred to as a coccus, as its name indicates. Staphylococcus aureus is the most pathogenic species of the Staphylococcus genus. It is responsible for food poisoning and for suppurative localized infections. Pseudomonas aeruginosa is a gram-negative bacterium of the Pseudomonas genus. The bacilli are thin, straight and very mobile owing to a polar flagellum. It is pathogenic and commonly encountered in nosocomial infections.
Fungi are eukaryotes with a nucleus surrounded by a membrane and containing the chromosomes. Two types thereof exist, yeast and moulds. Candida albicans is the most important and most well-known yeast species of the Candida genus. It is an organism which lives naturally in the mouth and the digestive tract of human beings. It is found in 80% of the population, and it does not usually lead to any particular disease or symptom. It is a saprophytic commensal organism which becomes pathogenic if the carrier organism becomes weakened. The mould studied is Aspergillus niger. It is very widespread (fruit and vegetables that have gone moldy, fodder, dairy products). It is widely used in the food-processing industry for the production of various acids. This species can be pathogenic (aspergillosis of the auditory canal, production of ochratoxin).
There are a very large number of possible sources of microbial contaminations of topical products. The microorganisms originate mainly from humans or from the environment, and intervene at various times of the processing, storage or use of the product.
Those formulating pharmaceutical compositions must therefore integrate this problem very early into the development of a topical composition. The addition of a preservative is often the solution adopted.
An antimicrobial preservative is a substance or a set of substances which is added intentionally to a formulation in order to prevent the proliferation of microorganisms. These preservatives should be introduced in a small amount, have a broad spectrum of action and be devoid of toxicity, and should not offset the efficacy of the active ingredients used.
A preservative agent does not always have a spectrum of activity that is broad enough to inhibit all the microorganisms indicated above. For this reason, combining said preservative agents according to their activity is a commonly used approach. By combining them correctly, the preservative system obtained acts on all the microorganisms.
A large variety of antimicrobial preservative agents that can be used in topical products exists. However, while this list is long for products for cosmetic applications, it is restricted for pharmaceutical products. In fact, only about ten preservatives are normally employed in this environment.
This difference comes from the fact that, during the clinical study, the pharmaceutical products must be completely tolerated by or completely innocuous to humans.
The preservatives normally employed in the pharmaceutical field are, for example, formaldehyde-generating agents, such as imidazolidinylurea or diazolidinylurea, thiazins derivatives, such as Kathon™ CG (methylchloroisothiazolinone (MCI)), chlorinated derivatives, such as chlorhexidine, phenolic derivatives, such as parabens, alcoholic derivatives, such as bronopol, phenoxyethanol or chloroxylenol, acid derivatives, such as sorbic acid or benzoic acid, or benzaikonium chloride.
The preservatives which are preferred and more conventionally included in pharmaceutical compositions are parabens, in particular methylparaben, propylparaben, ethylparaben or butylparaben, and phenoxyethanol, alone or as mixtures.
The most common preservative agents are parabens, ideally combined with phenoxyethanol.
However, phenoxyethanol can become a substance that is toxic to the user at high doses. For healthy individuals, the concentrations necessary for toxicity are high. However, phenoxyethanol is a recognized allergen. The use thereof can cause eczema plaques in certain individuals.
Moreover, the parabens themselves also exhibit toxicity at high doses.
In general, those skilled in the art are aware that the preservatives normally employed in topical formulations can be potentially sensitizing, irritant and/or allergenic. For all these reasons, it becomes important to limit their use or even to completely remove them from the formulations. However, if a preservative system is not added, the antimicrobial protection will not be effective. For this reason, it is important to determine another approach that can provide this function.
Certain factors, such as the temperature of the medium, the pH or the water content, influence the colonization by microorganisms, and those skilled in the art have studied the possibility of modifying these factors. The temperature of the medium does not have a really bactericidal or fungicidal effect. Bacteria develop at around 32.5° C. and fungi around 22.5° C. If a formulation is stored above or below these temperatures, for example in a refrigerator at +4° C., the microorganisms will become dormant and will not develop. If the temperature becomes favorable again, the microorganisms will once again be able to grow. Maintaining at high temperature (>+75° C.) or low temperature (<+4° C.) presents numerous constraints, whether during production or during use.
If the pH of the composition is very acidic or very basic, microorganism development will be limited. However, moulds are tolerant to a very broad pH range, and thus the development thereof will nevertheless be possible. The use of a topical composition at high or low pH also has its limits. This is because the application of a very acidic or basic solution or cream to the skin can have irritant effects.
The water content is also a very important point. This is because the presence of water is essential for the proliferation of microorganisms. Thus, if the medium is completely anhydrous, their proliferation will be inhibited. However, those skilled in the art in the pharmaceutical and cosmetic sector cannot envisage only anhydrous compositions, which are very often not as pleasant as emulsion or gel compositions. Moreover, many pharmaceutical active ingredients are water-soluble and therefore require the presence of water in the compositions. Without having to eliminate the water, those skilled in the art must take into account the water activity in the composition. The water activity is not exactly the amount of water, but the amount of free water in a medium. The free water is the water which does not serve to solvate the molecules introduced into the aqueous medium.
This free water is therefore completely accessible to the microorganisms in order to provide proliferation thereof.
The water activity (aw) is an intrinsic value of the medium studied, it does not depend on any external parameter. The aw ranges from 1.00 for pure water to 0.00 for a completely anhydrous medium.
The water requirements of each of the microorganisms is different. Bacteria, for example, are more sensitive to the presence of water than moulds.
Table 1 below is the water activity required for various microorganisms in order for them to develop.
TABLE 1Values of water activity necessary formicroorganism growth:MicroorganismWater activityAverage for bacteria0.91Pseudomonas aeruginosa0.97Escherichia coli0.95Staphylococcus aureus0.86Average for yeast0.86Candida albicans0.88Average for moulds0.80Aspergillus niger0.77
Thus, if the aw is less than 0.77, the microorganisms set forth in this table will not be able to develop.
It therefore becomes important to be aware of the means which induce a reduction in water activity.
The first, and the most obvious, is to reduce the amount of water introduced into the formulations.
The second comprises determining molecules that would have a considerable solvating capacity. Thus, the water would be mobilized to a greater extent in order to solvate these molecules and would be less available for the microorganisms. Humectants, mineral salts and hydrocolloids may play this role.
The measurement of the water activity of formulations has very recently been the subject of a chapter of the general methods of the U.S. pharmacopoeia (“Application of water activity determination to nonsterile pharmaceutical products <1112> USPC Official May 1, 2007-Jul. 31, 2007, 2007”).
The literature describes self-preservative compositions and lists excipients that are known to have a preservative activity. Thus, Jon J. Kabara (and D. S. Orth in “Preservative-free and self-preservative Cosmetics and Drugs—Principles and Practice”, published by Dekker, New York, 1996) lists various categories of excipients capable of having a preservative activity in the composition, such as alcohol, surfactants, fatty esters or acids, phospholipids, antioxidants or chelating agents. However, a large number of these ingredients taken alone or as a mixture fail to meet the criteria required by the pharmacopoeias, or meet them at concentrations that are not acceptable in a pharmaceutical composition. They cannot therefore be used as such and readily by those skilled in the art faced with the regulatory requirements, in pharmaceutical compositions.
The most active surfactants are cationic surfactants. However, the latter can essentially be included in compositions in the form of shampoos, a pharmaceutical form that is not a major one in the sector. In fact, those skilled in the art more particularly formulate emulsions or gels.
Moreover, J. J. Kabara has described that the proliferation of microorganisms can be prevented with ethanol, but starting from 25% (v/v). However, on the one hand, these percentages are extremely high for good tolerance of a topical pharmaceutical composition, and, on the other hand, nothing in the literature confirms the reductions actually observed for each microorganism, as must be the case in accordance with the pharmacopoeias.
The problem addressed by the present invention is therefore that of finding an alternative to the conventional preservatives in order to effectively protect a pharmaceutical, topical composition against the microorganisms indicated above.
The term “known preservatives” means, for example, formaldehyde-generating agents, such as imidazolidinylurea or diazolidinylurea, thiazins derivatives, such as Kathon™ CG (methylchloroisothiazolinone (MCI)), chlorinated derivatives, such as chlorhexidine, phenolic derivatives, such as parabens, alcoholic derivatives, such as bronopol, phenoxyethanol or chloroxylenol, acid derivatives, such as sorbic acid or benzoic acid, or benzalkonium chloride.
The preservatives most commonly formulated into compositions, in particular by the assignee hereof, are parabens, in particular methylparaben, propylparaben, ethylparaben or butylparaben, and phenoxyethanol, alone or as mixtures.
The problem addressed by the invention is therefore that of limiting, or even eliminating, the preservatives in a pharmaceutical topical composition.
A particular problem that must be solved by the invention is that of effectively protecting a pharmaceutical topical composition while at the same time meeting the criteria required by the European and U.S. pharmacopoeias. This is because, since the purpose of the pharmaceutical composition is to become a pharmaceutical product with a marketing authorization, it is imperative for the composition according to the invention to meet these criteria. In order to verify this point and to determine the antimicrobial action of the various mixtures of excipients according to the invention, a test protocol, known as the PET (Preservative Efficacy Test), exists. The PET comprises artificially inoculating the compositions with a known number of microorganisms, and then determining the decrease in the latter in the compositions tested, at given times. The protocol of this test is set up in order to abide by the recommendations of the European and U.S. pharmacopoeias. The test and also the recommendations of the European and U.S. pharmacopoeias are described in Example 1 to follow. The mixture of excipients as preservatives, described herein, should therefore meet the criteria of these pharmacopoeias in the PET.